Limbing assemblies of the type described above are normally included in such one-grapple harvesters as are used in mechanized forestry for felling, limbing and cutting trees into suitable lengths, both in stands with young trees and in stands for final felling. Certain prior art one-grapple harvesters have relied on the use of a so-called breast part which is moved in and applied to the stem of a standing tree, whereupon a plurality of arcuate or jaw-shaped gripping arms articulated to the breast part are swung in towards the stem for clamping and retaining it. Generally, the feeding units consist of spiked rollers which are pivotally connected to the breast part and which, after the tree has been cross-cut, are swung in towards the stem together with the limbing tools in order to carry out the required limbing operation. Since there are trees of highly varying diameters (small trees may have a stem diameter of about 40 mm and large trees a diameter of above 400 mm) and also since the same tree has a stem diameter varying from butt end to top end, the paths of movement of both the limbing tools and the feed rollers that should closely engage the stem will become rather complicated since the stem is always engaging the breast part, and the centre of the stem is thus moved away from or closer to the breast part depending on the variations of the stem diameter. In practice, this means that the suspensions for the feed rollers and the limbing tools must be given a complicated and expensive construction, and also that the angles of application of the limbing tools are not always ideal, which in turn means that the resistance to limbing quite often becomes extremely great.
SE laid-open application No. 8105907-3 describes a one-grapple harvester comprising two spiked rollers mounted on arms which may be provided with limbing tools and which are movable towards and away from each other, not only by being pivotal about joints or shafts but also by being linearly movable in srch a manner that the pivot shafts can be moved towards or away from each other. In this construction, the spiked rollers are however fixedly or stationarily mounted on the associated pivot arms, more specifically with their axes of rotation located in planes at right angles to the pivot shafts of the arms. By being fixedly mounted on the pivot arms, the stem-feeding spiked rollers may easily prove insufficient when a considerable limbing resistance arises. Thus, the limbing tools fixedly mounted on the arms and spaced from the spiked rollers in the feeding direction may encounter an unevenness or protuberance on the stem, for instance a large outgrowth which may appear in conjunction with a whorl of branches on the stem, while the spiked rollers are at the same time engaging a stem portion located behind which is at least slightly thinner than the stem portion with the protuberance which the limbing tools are engaging. As a result, the limbing tools are often liable to get stuck and the spiked rollers to slip.